It has been proposed that a vehicle seat occupancy condition is determined for an appropriate operation of a vehicle occupant protection system, such as an air bag system. The seat occupancy condition includes presence or absence of an occupant in a vehicle seat, an adult or a child, and a physique of the occupant. To determine the seat occupancy condition, several different methods are proposed.
One method is determining the condition by detecting variations in load applied by the occupant using pressure sensors arranged in a seat. Other methods include determining the condition by measuring a hip size of the occupant and calculating a sum of applied pressures, and by measuring the weight of the occupant using strain sensors.
The condition can be accurately determined by the above methods if the occupant is properly seated. However, the condition may not be accurately determined if a part of the hip is lifted due to a wobble of the vehicle or an accelerated velocity as in a case that the vehicle turns at high speed. That is because the measured weight or hip size of the occupant varies in such a case. Therefore, the condition may not be accurately determined. When the inaccurately determined condition is sent to the air bag system, improper air bag deployment may be performed.
To solve the problem, it is proposed that a physique of the occupant is detected in a condition that the occupant is properly seated in a vehicle seat with a seatbelt fastened. The detected physique is stored as physique data. One of such kind is proposed in JP-A-2000-302003. The physique is always accurately detected because a measurement performed for the detection is not affected by the wobble or the accelerated velocity. Thus, appropriate physique data is always available for air bag deployment control.
In the above device, the physique data is stored only when the seatbelt is fastened. Therefore, the appropriate physique data is not stored if the occupant does not properly fasten the seatbelt.